JP2921026B2 - Tetrafluoroethylene copolymer and method for producing the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a melt-moldable tetrafluoroethylene copolymer having good processability and thermal stability, and more particularly, to tetrafluoroethylene. The present invention relates to a copolymer in which a thermally unstable group existing at the terminal of the copolymer is stabilized and a method for producing the copolymer.

[Prior art] A copolymer of tetrafluoroethylene and perfluoro (alkyl vinyl ether) (hereinafter referred to as PFA) is well known as a melt-moldable fluororesin, and is used for covering tubes, pipes, joints, containers, electric wires. It is widely used for molding such as, or for rotational molding for producing coating, lining, and hollow molded articles.

Due to the polymerization mechanism, such PFA has -C at the terminal of the copolymer.
In the emulsion polymerization using a polymerization initiator such as ammonium persulfate (APS), a small amount of OF group is formed, and a -COOH terminal group is generated.
Alternatively, when methanol is used as a molecular weight regulator,
Groups such as CH ₂ OH or -COOCH ₃ occurs at the end. It is known that these terminal groups are thermally unstable, cause foaming and the generation of fluoric acid during molding, and cause molding failure and corrosion of a mold of a molding machine.

Therefore, techniques for stabilizing these unstable terminal groups have been studied, and some proposals have been made. For example, Japanese Patent Publication No. Sho 61-98709, -CONH ₂ end at least 50% of -COF and -COOH end groups in the PFA to thermally stabilize the -CH ₂ OH present as end groups Contacting PFA with ammonia gas or a nitrogen compound capable of producing ammonia for a time sufficient to be converted to a group;
Thermally stable at least 15 carbon 10 per ⁶ carbon -CH ₂ OH
A method for producing a multi-piece PFA is disclosed.

Japanese Patent Application Laid-Open No. 62-104822 discloses that PFA containing more than 6 -CF ₂ CH ₂ OH, -CONH ₂ and -COF terminal groups per 10 ⁶ carbon atoms has a carbon number of 10 or more. 10 ⁶ per 6
Disclosed is a method of contacting with a fluorine-containing gas under conditions of temperature, time and pressure sufficient to reduce the number to less than one.

[Problems to be Solved by the Invention] The present inventors produced PFA in which unstable terminal groups were stabilized based on these proposals, and formed it by a rotational molding method. It was found that the shrinkage was large and there was a problem in dimensional stability. Further, in the fluorination method disclosed in Japanese Patent Application Laid-Open No. 62-104822, a long-time reaction at a high temperature is required in order to increase the conversion efficiency. However, if such conditions can be alleviated as much as possible, it is economically and safely advantageous.

[Means for Solving the Problems] As a result of various studies on a method for treating an unstable terminal group, the present inventors have found that perfluoro (alkyl vinyl ether) is 1 to 10%.
Weight percent PFA in contact with fluorine gas -COF
And carbon atoms to the total number of -COOH end groups 10 ⁶ per 7-4
A method of completely converting -COF into -CONH ₂ by contacting with ammonia gas, and
The number of NH ₂ terminal groups is the number 10 7-20 pieces ⁶ per carbon -
Excluding CH ₂ OH and -COF, melt viscosity at 372 ° C
The present inventors have found that a stabilized PFA having a concentration of 0.1 × 10 ^{4 to} 100 × 10 ⁴ poise can solve the above-mentioned problems, and completed the present invention.

[Action] is unstable terminal group of PFA -CH ₂ OH or -COOH, -COOCH ₃
Changes to -COF when it comes into contact with fluorine gas, and finally -C
It becomes F _3. In the course of this change, a state occurs in which the oxygen-containing end groups are only -COF and -COOH. In the present invention, among the states, the total number of -COF and -COOH is 7 to 10 per 10 ⁶ carbon atoms.
Stop contact with fluorine gas when it reaches 40 stages. Therefore, conditions such as the time, temperature, and pressure of the treatment with fluorine can be relaxed, which is advantageous in both economic efficiency and stability.

Then although for contact with ammonia gas, resulting converted -COF is cut and all the -CONH _2, -COF in PFA
A -CH ₂ OH end groups no longer exist, -CONH ₂ end groups also becomes several 10 7 to 20 to ⁶ per carbon. The obtained PFA may contain fluorine ions in the form of ammonium fluoride.

As is clear from the examples described later, when the number of -CONH ₂ terminal groups is in the range of 7 to 20 per 10 ⁶ carbon atoms,
Foaming during molding is greatly reduced. Further, when the number of -CONH ₂ terminal groups decreases, the shrinkage of the obtained molded article increases.

EXAMPLES Hereinafter, preferred embodiments of the present invention will be described.

The PFA targeted by the present invention is a mixture of tetrafluoroethylene and a perfluoro (alkyl vinyl ether) represented by the formula: Rf—O—CF ＝ CF ₂ (where Rf is a perfluoroalkyl group having 3 to 4 carbon atoms). A copolymer with at least one kind, wherein perfluoro (alkyl vinyl ether) is
About 10% by weight. As the perfluoro (alkyl vinyl ether), those having a perfluoroalkyl group having 3 to 4 carbon atoms are preferable, and examples thereof include perfluoro (propyl vinyl ether) and perfluoro (butyl vinyl ether). The shape is powder,
It may be in the form of pellets, flakes, or the like.

The process of the present invention comprises a first step of treating PFA containing unstable terminal groups with fluorine gas and a second step of treating ammonia gas with PFA.

The first stage fluorine gas treatment is performed by contacting PFA with fluorine gas at a temperature of usually 150 to 250 ° C, preferably up to 200 ° C for 1 to 10 hours, preferably 2 to 5 hours. The pressure may be in the range of 1 to 10 atm, but usually atmospheric pressure is employed. Pure fluorine may be used as the fluorine gas, but from the viewpoint of safety, a diluted fluorine gas diluted with an inert gas to 5 to 25% by volume, preferably 7 to 15% by volume is preferable. Examples of the inert gas include nitrogen gas, argon gas, and helium gas. Fluorine gas treatment of the first stage and -COF and total 7-40 amino several 10 ⁶ per carbon of -COOH end groups in PFA. Therefore, compared with the method described in JP-A-62-104822 in which the terminal group is almost completely fluorinated, the treatment can be carried out at a lower temperature and in a shorter time.

In the second step of the process of the present invention, the PF obtained in the first step
A is brought into contact with ammonia gas and -COF is completely -CONH ₂
Convert to It is preferable to wash PFA with an inert gas such as nitrogen gas before passing ammonia gas. The ammonia gas to be contacted is 100%, and may be diluted to about 5 to 50% by volume with an inert gas. The treatment time is not particularly limited, but is usually 0.5 to 5 hours, preferably 60 to 90 minutes. The temperature and the pressure are not particularly limited, and each is usually 0 to 100 ° C., preferably room temperature, and usually 0.5 to 100 ° C.
1010 atm, preferably atmospheric. The reaction of the second stage proceeds rapidly, -COF are all converted to -CONH _2. As a result, Erareru PFA does not contain any -COF and -CH ₂ OH, -CONH ₂ is several 10 7 to 20 to ⁶ per carbon.

The PFA thus obtained contains 1 to 10% by weight of perfluoro (alkyl vinyl ether) and has a melt viscosity at 372 ° C. of 0.1 × 10 ^{4 to} 100 × 10 ⁴ poise.
This PFA has little foaming at the time of molding, has a small shrinkage of a molded product, and has high dimensional stability.

The analysis of the type and number of the terminal groups and the measurement of the melt viscosity in this specification are performed by the following methods.

(Analysis of terminal group) PFA powder is compression molded at 350 ° C for 30 minutes and thickness is 0.25-0.3m
The film of m is analyzed by infrared absorption spectrum, the type is determined by comparing with the infrared absorption spectrum of a known film, and the number is calculated from the difference spectrum by the following equation.

The correction coefficient of the target terminal group is shown below.

End group absorption frequency (cm ^-1) calculating a correction factor _{-COF 1883 440 -COOH 3560 440 -COOCH 3} 1795 400 -CONH 2 3436 460 -CH 2 OH 3648 2300 The correction factors are end groups having 10 per ⁶ carbon For this purpose, the determination was made from the infrared absorption spectrum of the model compound.

The infrared absorption spectrum analysis was performed by scanning 100 times using a Perkin Elmer FTIR spectrometer 1760X and a Perkin Elmer 7700 professional computer (both manufactured by Perkin Elmer).

(Measurement of melt viscosity) Using a high flow type flow tester manufactured by Shimadzu Corporation, the copolymer was charged into a cylinder with an inner diameter of 11.3 mm, and the temperature was 380 ° C.
After 5 minutes, 2.1m inside diameter under 7kg piston load
The material is extruded through an orifice having a length of 8 mm and a length of 8 mm, and the value obtained by dividing 53150 by the extrusion speed (g / min) at this time is determined as the melt viscosity.

Next, the present invention will be described based on examples, but the present invention is not limited to only these examples.

Example 1 A tetrafluoroethylene / perfluoro (propyl vinyl ether) copolymer (weight ratio: 97/3) was produced by an aqueous suspension polymerization method according to the method described in JP-A-58-189210. End groups of the obtained PFA is -CH ₂ OH, a -COOCH ₃ and -COOH, respectively the number of tens per ⁶ carbon 1
00, 43 and 2.

Place 15 g of this PFA in a special tray in a box-type reaction oven, close tightly, replace with sufficient nitrogen gas, and add 1.0 l of a mixed gas of fluorine gas and nitrogen gas (fluorine gas concentration 10% by volume).
At a flow rate of / min for 3 hours. The inside of the oven was set to atmospheric pressure, and the temperature was kept at 180 ° C. After the completion of the reaction, the heating was stopped and the gas was switched to nitrogen gas to sufficiently replace the fluorine gas for about 1 hour. At that time, the temperature was 30 ° C.

At this stage, the type and number of the terminal groups were examined.
F is 28 and -COOH is 3 (each is around 10 ⁶ carbon atoms)
In it, -CH ₂ OH and -COOCH ₃ had disappeared. The fluorine gas-treated PFA was subjected to ammonia gas treatment in a reaction oven by passing a mixed gas of ammonia gas and nitrogen gas (ammonia gas concentration of 50% by volume) at a flow rate of 2.0 l / min for 30 minutes. The temperature was room temperature (about 30 ° C). After the treatment, nitrogen gas was passed until the outlet gas became neutral, and the orb was opened to the atmosphere to take out the contents. The terminal group was analyzed and the melt viscosity was measured. The number of -CONH ₂ was 15 ( the number 10 per ⁶⁾ carbon, a melt viscosity of 7.5 × 10 ⁴ poise.

The above experiment was conducted using the same raw material PFA and changing the conditions of the fluorine gas treatment as shown in Table 1. The results are shown in Table 1. The above experimental example is described in Table 1 as sample No. 4.

In addition, the obtained fluorine ion extraction amount of PFA is also shown. To measure the amount of fluoride ion extraction, measure 10 g of a sample (pellet, film, powder, etc.), 5 ml of water and methanol
5 ml and 10 ml of the total ion concentration activity buffer were thoroughly mixed in a polyethylene bottle, allowed to stand for 24 hours, and then filtered,
The filtrate was measured with a fluorine ion meter (Publication No. 96-90-00, manufactured by Orion).

Example 2 Using the PFA powders of Sample Nos. 1 to 8 and the untreated (raw material) PFA (Sample No. 9) obtained in Example 1, rotational molding was performed, and the properties of the molded product (number of foams, shrinkage ratio, (Internal volume). The results are shown in Table 1.

(Rotation molding) After applying a mold release agent to a blast-treated rotation molding die (inner diameter: 161 mm) for bottle molding with an inner volume of 3 liters, 600 g of each sample was added, and the inside temperature was set in an oven set at 380 ° C. 1 hour rotation molding (rotation speed: revolution 9.4rpm, rotation 23rpm)
After cooling, a uniform 2 mm thick bottle molded product is taken out of the mold.

(Shrinkage ratio) Diameter D (mm) of molded product bottle obtained by the rotational molding
Is determined by the following equation.

(Internal volume) Fill the bottle with pure water and fill the bottle (ml)
Is measured with a measuring cylinder.

(Number of Foams) The molded article bottle is cut lengthwise with a knife, and the number of bubbles existing on the inner surface of the bottle is visually counted.

As is clear from Table 1, the number of -CONH ₂ end groups (number 10 per ⁶ carbon atoms) is 7-20 amino those (samples No.
In 2, 4, 5, and 6), foaming is small, and dimensional stability (shrinkage ratio) is in an acceptable range. Note that the relationship between the amount of extracted fluoride ions and the foaming or shrinkage ratio is not a clear correlation, but the foaming is less when the amount of extraction is to some extent.

Example 3 Sample Nos. 4 and 8 and Sample No. 9 obtained in Example 1
(Untreated) PFA powder is extruded with a melt indexer (MX-101, manufactured by Takara Kogyo Co., Ltd.).
It was cut every 2 mm, and the amount of extracted fluoride ions and the number of -COF terminal groups were examined (treatment 1).

Extrusion molding was also performed on the heat-treated sample of PFA that had been previously heat-treated (20 g of sample powder was placed in an aluminum cup and heated at 380 ° C for 5 hours in air), and the amount of fluoride ions extracted and the number of -COF end groups were determined. (Process 2).

 The results are shown in Table 2.

Table 2 shows that the PFA of the present invention has a small increase in the amount of extracted fluoride ions and the number of -COF terminal groups even when heated, and is thermally stable.

[Effects of the Invention] According to the present invention, PFA which is thermally stable and has excellent powder properties
Can be provided, and a molded article obtained by using this product has little foaming and excellent dimensional stability.

Continued on the front page (72) Inventor Toshio Miyatani 1-1, Nishiichitsuya, Settsu-shi, Osaka Daikin Industries, Ltd. Yodogawa Works (58) Field surveyed (Int. Cl. ⁶ , DB name) C08F 214/26 C08F 8/22 C08F 8/30

Claims (2)

(57) [Claims] 1. A tetrafluoroethylene formula: Rf-O-CF = CF 2 ( wherein, Rf is a perfluoroalkyl group having 3 to 4 carbon atoms)
Perfluoro (alkyl vinyl ether) represented by
A copolymer with at least one of the following, comprising 1 to 10% by weight of perfluoro (alkyl vinyl ether) units,
The number of -CONH ₂ terminal groups is 7 to 20 per 10 ⁶ carbon atoms, does not include -CH ₂ OH and -COF, and has a melt viscosity at 380 ° C of 0.1 × 10 ^{4 to} 100 × 10 ⁴ poise. Tetrafluoroethylene copolymer. 2. Theofluoroethylene and the formula: Rf—O—CF−CF ₂ (wherein, Rf is a perfluoroalkyl group having 3 to 4 carbon atoms)
Perfluoro (alkyl vinyl ether) represented by
A copolymer comprising 1 to 10% by weight of a perfluoro (alkyl vinyl ether) unit, and contacting the copolymer with fluorine gas to obtain a total number of -COF and -COOH end groups. To 7 to 40 per 10 ⁶ carbon atoms, and then contact with ammonia gas to
Preparation of the tetrafluoroethylene copolymer of claim 1 wherein the converting the COF fully into -CONH _2.